The cell
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Graded potentials are short-distance signals (see Table 1.3). They are local changes in the membrane potential that occur at synapses, where one neuron connects with another neuron. The magnitude of these signals varies with the strength of the stimulus. As the intensity of the stimulus increases, the number of ions diffusing across the cell membrane increases and the magnitude of the change in the membrane potential increases. This change may be in either direction such that the membrane potential may become more negative or less negative compared to the resting membrane potential (see Figure 1.4). Depolarization occurs when the membrane potential becomes less negative, moving toward zero. As will be discussed, depolarization makes the neuron more excitable. Hyperpolarization occurs when the membrane potential becomes more negative, moving farther away from zero. Hyperpolarization tends to make the neuron less excitable. These signals are transient or short-lived. Once the stimulus has been removed, the membrane potential returns to its resting state. Following a depolarization, the membrane is said to undergo repolarization and a return to its resting potential.
The Cell Membrane in the Steady State
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
The change in membrane conductance could be caused by: Physical stimuli, such as mechanical deformation, as in touch receptors and muscle receptors, or light in the case of photoreceptors.Chemical stimuli, as in taste and smell receptors as well as in nerve and muscle cells, whereby the binding of ligands to specific receptors on the outer or inner surface of the membrane change membrane conductance.Membrane depolarization, which affects membrane conductances in a specific manner, as discussed in the next chapter.
Daptomycin
M. Lindsay Grayson, Sara E. Cosgrove, Suzanne M. Crowe, M. Lindsay Grayson, William Hope, James S. McCarthy, John Mills, Johan W. Mouton, David L. Paterson in Kucers’ The Use of Antibiotics, 2017
The specific mechanisms leading to bacterial cell death remain, however, unclear. The changes in cell membrane homeostasis lead to leakage of ions and loss of cell membrane potential (Pogliano et al., 2012). A correlation between dissipation of membrane potential and the bactericidal activity of daptomycin was demonstrated by Silverman et al. (2003). Membrane depolarization was measured by both fluorimetric and flow cytometric assays. Adding daptomycin (5 mg/l) to S. aureus gradually dissipated membrane potential. In both assays, cell viability was reduced by > 99% and membrane potential was reduced by > 90% within 30 minutes of adding daptomycin. Cell viability decreased in parallel with changes in membrane potential, demonstrating a temporal correlation between bactericidal activity and membrane depolarization. Decreases in viability and potential also showed a dose-dependent correlation. Depolarization is indicative of ion movement across the cytoplasmic membrane. Fluorescent probes were used to demonstrate Ca2+-dependent, daptomycin-triggered potassium release from S. aureus. Potassium release was also correlated with bactericidal activity (Silverman et al., 2003).
Spider toxins targeting ligand-gated ion channels
Published in Toxin Reviews, 2021
Purinergic receptors are activated by nucleotides and constitute LGIC (P2X) (Valera et al. 1994) and metabotropic (P2Y) receptors (Webb et al. 1993). P2X receptors are nonselective cation channels activated endogenously by ATP, and permeable to sodium and calcium (Egan and Khakh 2004). The activation of the channels leads to the membrane depolarization (Erb et al. 2006). There are seven cloned human subunits: P2X1-7. Each subunit consists of intracellular N- and C-termini, two transmembrane domains (TM1 and TM2), and large extracellular domain (Habermacher et al. 2016, North 2016) (Figure 5). The intracellular domains contain consensus phosphorylation sites for protein kinases and were shown to be modulated by protein kinases PKA and PKC (Boue-Grabot et al. 2000, Brown and Yule 2010). The TM1 domain gates the channel while TM2 lines the channel pore. The extracellular domain contains orthosteric ATP-binding site as well as a site that permits allosteric modulation of the receptor by cations such as zinc, copper, magnesium and others (Roberts et al. 2006, Coddou et al. 2011, Coddou et al. 2011, Chataigneau et al. 2013).
Marine peptides as immunomodulators: Californiconus californicus-derived synthetic conotoxins induce IL-10 production by regulatory T cells (CD4+Foxp3+)
Published in Immunopharmacology and Immunotoxicology, 2019
Daniela Zazueta-Favela, Luis Donis-Maturano, Alexei F. Licea-Navarro, Johanna Bernáldez-Sarabia, Kee W. L. Dan, Julián M. Cota-Arce, Galileo Escobedo, Marco A. De León-Nava
Wang et al., found that specific activation of α7nAChR could significantly block NF-kB (Nuclear Factor kappa B) signaling [33,36], which in turn can promote anti-inflammatory effects. Stimulation of nAChR opens channels and induces an inflow and outflow of ions such as calcium. After the membrane depolarization, voltage-operated calcium channels are opened, leading to an additional flow of calcium ions. This influx causes secretion of mitogenic factors and activates cell signaling cascades [32]. Besides, the interaction between ligand-receptor is essential for activation, cell differentiation, secretion of cytokines, among others processes [37]. It has been demonstrated that Treg lymphocytes express the α7 subunit in their nicotinic receptors and that stimulation with their ligand potentiates the suppressor activity of these cells, preventing the proliferation of CD4+ T lymphocytes in vitro [38]. Considering the possibility that these conotoxins specifically interact with the α7 subunit of nAChR, the assumption is that Treg, through an increase of IL-10, inhibit the proliferation of lymphocytes, thus no change in the number of cells was observed. Nowadays, treatment with this cytokine is studied as a possible therapy against cancer variants [39] and because some inflammatory diseases exhibit defective IL-10 secretion [40].
Efficient simulations of stretch growth axon based on improved HH model
Published in Neurological Research, 2023
Xiao Li, Xianxin Dong, Xikai Tu, Hailong Huang
Because neural cells can produce action potentials, a regenerative electrical signal whose amplitude does not fade as it travels down the axon, is capable of transmitting signals over extended distances [19]. Electrical signals play a critical role in the transmission of nerve signals. When the depolarization of the membrane at any point along the axon exceeds a threshold value, an action potential is generated in that region in response to the opening of voltage-gated sodium ion channels. Local depolarization propagates electrically along the axon, forcing surrounding membrane areas to exceed the threshold for generating additional action potentials. As a result of the potential differential between the active and inactive sections of the axonal membrane, depolarization propagates throughout the length of the axon via a ‘local loop’ of current.
Related Knowledge Centers
- Action Potential
- Hyperpolarization
- Membrane Potential
- Physiology
- Resting Potential
- Sodium
- Ion Channel
- Cell
- Ion
- Sodium–Potassium Pump